fix bug with features sometimes disappearing when scrolling.
fix bug with features sometimes disappearing when scrolling.

That one led me a merry chase.  I think I shall be picking burrs and
dressing bramble scratches for quite some time.

GreggHelt2/apollo-test,Arabidopsis-Information-Portal/jbrowse,GreggHelt2/apollo-test,SuLab/jbrowse,limeng12/jbrowse,limeng12/jbrowse,igemsoftware/Shenzhen_BGIC_0101_2013,nathandunn/jbrowse,GreggHelt2/apollo-test,igemsoftware/Shenzhen_BGIC_0101_2013,igemsoftware/Shenzhen_BGIC_0101_2013,nathandunn/jbrowse,erasche/jbrowse,limeng12/jbrowse,erasche/jbrowse,limeng12/jbrowse,Arabidopsis-Information-Portal/jbrowse,GMOD/jbrowse,limeng12/jbrowse,SuLab/jbrowse,Arabidopsis-Information-Portal/jbrowse,nathandunn/jbrowse,igemsoftware/Shenzhen_BGIC_0101_2013,Arabidopsis-Information-Portal/jbrowse,erasche/jbrowse,limeng12/jbrowse,Arabidopsis-Information-Portal/jbrowse,GMOD/jbrowse,erasche/jbrowse,igemsoftware/Shenzhen_BGIC_0101_2013,SuLab/jbrowse,GreggHelt2/apollo-test,igemsoftware/Shenzhen_BGIC_0101_2013,SuLab/jbrowse,SuLab/jbrowse,erasche/jbrowse,SuLab/jbrowse,GreggHelt2/apollo-test,igemsoftware/Shenzhen_BGIC_0101_2013,GMOD/jbrowse,GMOD/jbrowse,igemsoftware/Shenzhen_BGIC_0101_2013,Arabidopsis-Information-Portal/jbrowse,SuLab/jbrowse,limeng12/jbrowse,GMOD/jbrowse,nathandunn/jbrowse,Arabidopsis-Information-Portal/jbrowse,erasche/jbrowse,GreggHelt2/apollo-test,nathandunn/jbrowse,limeng12/jbrowse,GreggHelt2/apollo-test,erasche/jbrowse,erasche/jbrowse